ECO Cavity wall U-value briefing

Background

Ofgem have tightened up the criteria for accepting amended U-values in SAP and RdSAP calculations used in the measurement of carbon savings for the ECO programme (Energy Company Obligation). Previously, where a U-value other than the default value was used in calculations the U-value had to be calculated or verified by a suitably qualified person.

Evidence of suitable qualification was through membership of a recognised U-value calculation competency scheme (BBA/TIMSA), OCDEA membership (approved organisation in Scotland) or any other scheme formally agreed between Accreditation Schemes/Approved Organisations and Government. (This definition is from RdSAP convention 3.08).

New compliance methods

Ofgem have now introduced threshold values so non-default U-values below the threshold should still be calculated in the same way, with a suitably qualified person calculating or verifying. However, where the non-default U-value is higher than the threshold the calculation is subject to more stringent conditions. There are three possible methods for obtaining an acceptable calculation:

The calculation has to be produced or verified by a suitably qualified person based on either:

• design or construction specifications obtained from the design or construction team; or • laboratory-tested performance values obtained from samples of the construction materials.

The calculation has to be produced or verified by:

• a member of the BBA/TIMSA U-value competency scheme; or
• a member of another agreed scheme (of which there are currently none).

A building control approval (presumably part of a full plans deposit) which states the construction and the calculated U-value.

The first route does not require any additional qualification in the person carrying out the assessment, but information gathering will be onerous. It is unlikely that the design or construction specifications would be available, while obtaining and testing samples would be expensive and time consuming. The third route will only apply in a very small number of cases where the original building control documentation is still available.

The second option effectively requires the person carrying out or verifying the calculation to be a member of the BBA/TIMSA U-value competency scheme.

BBA/TIMSA U-value competency scheme

The U-value competency scheme set up by the BBA in conjuction with TIMSA (Thermal Insulation Manufacturers and Suppliers Association) is the only audited competency scheme for U-value calculations in the UK.

Organisations join the scheme and then appoint one or more competent persons who have to be assessed and approved by the BBA. The competent persons do not have to carry out all the U-value calculations issued under the scheme, but they are responsible for their accuracy. The BBA carries out annual audits of the calculations issued by competent persons.

JPA TL software and training

The JPA Designer U-value module is ideal for carrying out U-value calculations as part of the competency scheme. The calculator follows the conventions in BR 443 (Conventions for U-value Calculations) and contains product data from sources required by the scheme.

JPA TL has trained many of the schemes competent persons, and is able to offer comprehensive training and support through the assessment procedure. The training covers hand calculation of U-values using he combined method, which is a key part of the accreditation process. The training can be delivered face-to-face, or as a distance learning course. More details and costs are given here.